This invention relates generally to fluid control valves and, more particularly, to fluid control valve structures which suppress the noise normally generated by fluid flow through a control valve.
One type of prior art fluid control valve includes a valve body having inlet and outlet ports, a sleeve-like cage, a valve plug that is slidable within the cage and a bonnet assembly which retains the cage and the valve plug in the valve body. The inlet port communicates with the outlet port through apertures, or windows, in the cage. Fluid flow through the valve is determined by the position of the valve plug relative to the windows of the cage. A valve stem attached to the valve plug extends through the bonnet assembly to an actuator for moving the valve plug relative to the cage. An example of a prior art fluid control valve is disclosed in U.S. Pat. No. 3,776,278, issued Dec. 4, 1973 to Allen. Additional fluid control valves are disclosed U.S. Pat. No. 5,769,122, issued Jun. 23, 1998 to Baumann et al; U.S. Pat. No. 5,941,281, issued Aug. 24, 1999 to Baumann et al; and U.S. Pat. No. 6,095,196, issued Aug. 1, 2000 to McCarty et al.
Prior art fluid control valves have provided satisfactory performance but have certain drawbacks. The valve may generate undesirable noise under certain flow conditions, such as a high pressure drop through the valve. U.S. Pat. No. 3,776,278 discloses a valve structure for reducing noise in gas applications. In one embodiment, the cage is provided with slots having long dimensions parallel to the cage bore axis. The slots have their narrowest dimension intermediate their ends and taper or flare gradually to a wider dimension at the inner and outer surfaces. In another embodiment, the cage has closely-spaced, uniformly-distributed circular holes.
The disclosed valve structures reduce noise generation, but noise may continue to be a problem under certain operating conditions. Furthermore, the disclosed valve is designed for use only with gases. Accordingly, there is a need for valve structures for use with liquids and gases, which exhibit further reductions in noise generation and which have desirable flow characteristics.
According to a first aspect of the invention, a fluid control valve is provided. The fluid control valve comprises a valve body having a fluid passageway, a cage mounted in the fluid passageway, the cage including a wall defining a cage bore having an axis, and a valve plug assembly comprising a valve plug that is axially slidable in the cage bore. The cage defines one or more windows and a valve seat. Each of the one or more windows comprises a plurality of slots each having a longitudinal axis, wherein the longitudinal axis of each of the slots in parallel to or tilted at a relatively small angle with respect to a reference plane that is perpendicular to the cage bore axis and wherein the slots are axially spaced apart.
The longitudinal axes of the slots may be oriented at an angle in a range of about 0xc2x0 to 15xc2x0 with respect to the reference plane. In some embodiments, the slots are tilted at an angle of about 4xc2x0 with respect to the reference plane. In other embodiments, the slots are oriented parallel to the reference plane. In further embodiments, the slots in adjacent windows are tilted in opposite directions with respect to the reference plane. The slots may be tilted at an angle with respect to the reference plane to provide a relatively smooth flow progression between adjacent slots as a function of valve plug position along the cage bore axis.
Two or more of the slots may have different lengths to provide a desired flow characteristic. In some embodiments, the slots are relatively short in a portion of the cage adjacent to the valve seat and are relatively long in a portion of the cage spaced from the valve seat.
The slots may be tapered in width through the wall of the cage. Preferably, the slots increase in width with increasing radius through the wall of the cage. The slots may be tapered in width through the wall of the cage at an angle in a range of about 4xc2x0 to 17xc2x0.
The slots in the cage may be configured for low noise liquid flow toward the cage bore axis and for low noise gas flow away from the cage bore axis. For liquid applications, the valve plug preferably has a relatively small radial wall thickness in proximity to a seating surface in order to limit exposure of the valve plug to imploding jets when liquid flow into the cage is undergoing cavitation.
In one embodiment, the cage defines a sealing lip in the cage bore located above the windows, and the valve plug includes one or more pressure balancing passages between opposite ends thereof. The valve plug assembly further comprises an elastomer ring for engaging the sealing lip when the valve plug is in a closed position.
In another embodiment, the cage defines a sealing lip located in the cage bore above the windows, and the valve plug includes one or more pressure balancing passages between opposite ends thereof. The valve plug assembly further comprises a deformable sealing ring for engaging a sealing lip when the valve plug is in a closed position.
According to another aspect of the invention, a valve cage is provided for mounting in a fluid passageway of a fluid control valve. The valve cage comprises a generally cylindrical wall defining a cage bore having a axis. The wall defines one or more windows and a valve seat. Each window comprises a plurality of slots, each having a longitudinal axis. The longitudinal axis of each of the slots is parallel to or tilted at a relatively small angle with respect to a reference plane that is perpendicular to the cage bore axis.